Familiar Pink vs Cardinal Purple

How close are they?

ΔE 42.7, loose: different enough that you should pick on purpose. Cardinal Purple is a little darker, more muted, warmer than Familiar Pink.

Can I use Cardinal Purple instead of Familiar Pink?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 43). Cardinal Purple is a little darker, more muted, warmer than Familiar Pink.

Can I use Familiar Pink instead of Cardinal Purple?

The same difference applies the other way round: Familiar Pink is a little lighter, more saturated, cooler.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.